Oracle provides official VirtualBox personal package archive (PPA) to install it in Ubuntu 16.04. The PPA is provided from VirtualBox own server, not from Launchpad. This PPA in the time we write this article, has latest VirtualBox version 5.0.18. Here the procedures shown step by step.

1. Add The Repository Address

Perform an editing command: 
sudo gedit /etc/apt/sources.list
When Gedit window interface comes, enter this single line to a new line and save:
deb xenial contrib
Note: change the "xenial" name into your own Ubuntu codename wily for 15.10, vivid for 15.04, utopic for 14.10, trusty for 14.04, and so on, if you want to install VirtualBox in the older version of Ubuntu.

2. Add The Secure Key

Download the Oracle secure key file for Ubuntu apt-secure program here: The file name you download is oracle_vbox.asc. Place the file in your $HOME directory.

3. Add The Key Into System

Perform the apt-add command:
sudo apt-add orache_vbox.asc

4. Reload The Apt Database

Perform the reload command:
sudo apt-get update

5. Install VirtualBox

For the latest VirtualBox version, version family of 5.0, perform the install command below:
sudo apt-get install virtualbox-5.0
For the older VirtualBox version, version family of 4.3, perform the install command below:
sudo apt-get install virtualbox-4.3

Important Note

If you are facing error when performing install command, such as: 
Err:1 xenial/contrib i386 virtualbox-5.0 i386 5.0.18-106667~Ubuntu~xenial                    
  Connection failed [IP: 80]
E: Failed to fetch  Connection failed [IP: 80]
Then re-run the install command with --fix-missing option such as
sudo apt-get install virtualbox-5.0 --fix-missing
sudo apt-get install virtualbox-4.3 --fix-missing

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